Adequate bone quantity is one of the important factor to obtain osseointegration after implantation. Guided bone regeneration (GBR) has widely used in implantation for reconstruction of bony defects. Since introducing this procedure, there are many studies about survival rate of implants, changing in surrounding bone volume after function. The purpose of this study was to evaluate the amount of resorption according to placement timing and survival rate after function. The subjects were patients who had been operated with GBR from Jun 2003 to Jun 2004 in Seoul National University Bundang Hospital. They were divided into simultaneous and delayed placement group. The follow up had been performed at the time of just after GBR, 1, 3, 6, 12, 24-month later and standard periapical radiographs were taken to estimate the bone level at the time. The total average of bone level change in radiographs was 1.94mm(${pm}0.25$), and 1.92mm(${pm}0.72$) in simultaneous installation, 2.03mm(${pm}0.25$) in delayed installation. In this report, the survival rates were 92.2% in simulataneous group and 92.3% in delayed group. Insufficient primary stability, early contamination of wound, overloading, poor oral hygiene, and infection were thought to be associated factors in the failed cases.